Herpes Virology Research

Herpesviruses are a leading cause of human viral disease, second only to influenza
and cold viruses. Herpesviruses consist of a double-stranded (ds) DNA genome
contained within a protein shell, termed the capsid, that is surrounded by an
unstructured protein layer (the tegument) and a lipid-envelope. During viral
replication, an ATP-dependent motor packages the genome into a preformed capsid
through a unique opening created by the portal complex. Herpes Simplex virus type 1
(HSV-1) is a prototypical model system to study the general infection mechanisms of
herpesviruses and other viruses that release their genome into the cell nucleus
without capsid disassembly. We have recently shown that HSV-1 genome packaging
creates an internal pressure of tens of atmospheres within the viral capsid. This
pressure results from bending stress and repulsive forces acting on the tightly
packaged DNA molecule. We also found that despite its liquid crystalline state
inside the capsid, the DNA is fluid-like which facilitates its ejection into the
cell nucleus during infection. The fluidity or, equivalently, mobility of the
closely packaged DNA strands caused by interstrand repulsive interactions is
regulated by the ionic environment of the cellular cytoplasm.

Between rounds of replication, the virion must be sufficiently stable to ensure that
the packaged genome is retained within the capsid. Conversely, during infection the
virion must be unstable enough to allow genome release into the cell nucleus. A
precise balance between these physical aspects of the viral capsid and its
encapsidated genome is crucial to the viral replication cycle. Using HSV-1 as our
primary model system, we investigate the roles of intracapsid DNA mobility, internal
DNA pressure and capsid stability for viral replication with respect to retention of
the packaged genome inside the capsid and its subsequent ejection during infection. These studies provide new insights into the key mechanisms facilitating as well as
inhibiting viral infectivity.

Physical Virology of Herpesviruses and Phage

Viruses are simple lifeless entities that cannot reproduce on their own and therefore depend on host cells to provide them with the necessary life support mechanisms. Simplified, all viruses consist of a protein shell (capsid) that protects the viral genome (DNA or RNA). To infect, the viral genome must enter the cell, where it hijacks the host cell’s machinery and synthesizes multiple copies of virions. This can lead to cell lysis, which is a lethal event.

Physical virology is a rather new field that seeks to define the physical mechanisms controlling virus development. This knowledge can provide information essential to the rational design of new anti viral strategies with less specificity for a limited number of viruses. Furthermore, biological and physical simplicity relative to other biological systems have made viruses an attractive physical model system to study fundamental prosperities of DNA compaction and translocation as well as protein self-assembly using viral capsids.

Our Biophysical Tools

Evilevitch's physical virology group investigates fundamental physical principles that
control viral encapsidation and genome release. Our group has discovered a way to
determine genome pressure in viral capsid and found that to be as high as 20 atm in
human Herpes Simplex Type 1 virus, a pressure equivalent to that at a depth of 600
ft in the ocean. We are specifically interested in determining the physical nature
of genome packaging and release, the kinds of pressures involved, the strengths and
elastic properties of the capsids, and limits on the amount of material that can be
encapsidated. The main tools in the lab are: Atomic Force Microscopy (AFM),
microcalorimetry, high resolution cryo electron microscopy and single molecule
fluorescence, small angle x-ray scattering and light scattering.